1. Field of the Invention
The present invention relates to a process carried out in a reaction column for the chemical reaction of substances the reaction of which is affected by an unfavorable equilibrium position of the main reaction or a preceding equilibrium, wherein during the reaction one or more substances to be separated are continuously removed from the reaction mixture by one or more auxiliaries.
2. Description of the Prior Art
In the past, reactive distillation proved successful in processes wherein conversion is impaired by the position of the chemical equilibrium forming the basis for reaction. Besides the production of ethers which are used for example as antiknock additives in fuels, esterification is another field of application. Prior art processes of esterification are reactive distillation processes allowing continuous separation of the water from reaction by distillation. See e.g. J. Krafczyk and J. Gmehling, Chem. Ing. Tech., vol. 66 (1994), p. 1372; and C. Breucker, V. Jordan, M. Nitsche, and B. Gutsche, Chem. Ing. Tech., vol. 67 (1995), p. 430. During conventional reactive distillation the temperatures in the column are such that all substances, except for the bottoms, are heated to boiling point.
In the known processes, separation of the water from reaction is effected by a reactant which, in most cases, must be charged in high excess. It is therefore necessary that at the given pressure the temperature for separation be equal to or higher than the distillation temperatures of the reactants. The reactants employed in said processes are an auxiliary and an additional substance. In esterification processes the alcohol, if used in excess, is both the reactant for the esterification reaction and the auxiliary for removing the water from reaction. Furthermore, it is necessary to determine the ratio at which the reactants are used in order to achieve efficient separation. According to C. Breucker et al., separation of the water from reaction, if the reactants are present in low excess, is a challenging task for process engineers. Up to now, this problem has been tackled by using batch or cascade processes employing several reactors.
One embodiment which is well known in the art is the one-stage esterification using an entraining agent and taking advantage of azeotrope formation. See e.g. Organikum, VEB Deutscher Verlag der Wissenschaften, Berlin (1977), p. 71-73. Processes for producing esters from carboxylic acids and alcohols with continuous separation of condensed water in a column using entraining agents, such as benzene, methanol, and butyl alcohol are described in DE 976 413 B. The entraining agent used according to U.S. Pat. No. 2,384,793 is butane.
WO 94/19079 discloses a process for producing bisphenol A from acetone and phenol while splitting off water. The resultant water from the reaction is removed using an inert stripping gas. The aforesaid process employs a reactor containing a liquid catalyst or a particulate, suspended catalyst, while the reactor itself is equipped with trays, drains, and/or hold-back screens.